Network protocol concept

## Concept

Hypertext Transfer Protocol, Hypertext transfer ( Transfer ) agreement , It is a protocol formulated by the client and server to transmit text . structure WWW The specific three technologies are as follows ：

WWW: world wide web, web – HTML: Hypertext Markup Language, Hypertext markup language – HTTP: Hypertext Transfer Protocol, Hypertext transfer ( Transfer ) agreement (HTTP yes TCP/IP Application layer protocol ) – URL: Uniform Resource Locator, Uniform resource locator symbol

> URI: Uniform Resource Identitier, Unified resource identifier ,URL yes URI Subset

## TCP/IP

“` application layer (http/https/websocket/ftp…) => Definition ： Text transfer protocol | Transport layer (tcp/udp) => Definition ： port | The network layer (ip)　=> Definition ：IP | The link layer (mac& Data packets ) => Definition ： Data packets ,MAC Address | Physical layer ( optical cable / cable / Switch / route / terminal …) => Definition ： Physics “`

TCP/IP:

– Explain a ： Represent the tcp The protocol and ip agreement – Explain two ： If you follow the five layer network architecture ,TCP/IP Represents the general name of all protocol clusters except the application layer

TCP/IP connect: TCP/IP Three handshakes of : “` Be marked with syn Data packets of ————-> Be marked with syn/ack Data packets of client <————- server Be marked with ack Data packets of ————–> “`

TCP/IP finish: TCP/IP Four handshakes : “` fin <————- ack client( or server) ————-> server( or client) fin ————-> ack <————- “`

## HTTP message

HTTP The message consists of three parts : – Start Line – Headers – Entity Body

HTTP There are two types of messages : – Request message – response message

### Request message Start Line

grammar : < Method > < request URL> < edition >

#### HTTP Method

+ get: Access to resources , Do not carry http body, Support query parameters , size 2KB + post: Transfer resources ,http body, The default size is 8M,1000 individual input variable + put: Transfer resources ,http body, Resource update + delete: Delete resources , Do not carry http body + patch: Transfer resources ,http body, Existing resources are partially updated + head: obtain http header, Do not carry http body + options: Get supported method, Do not carry http body + trace: track , Return the request loopback information , Do not carry http body + connect: Establish tunnel communication

### response message Start Line

grammar : < Method > < Status code > < The reason the phrase >

#### HTTP Status Code

+ 200: ok + 301: Permanent redirection + 302: Temporary redirection + 303: Temporary redirection , Asked to use get Request resources + 304: not modified, Return cache , It has nothing to do with redirection + 307: Temporary redirection , Strict disobedience post To get + 400: Parameter error + 401: Not through http authentication + 403: forbidden, unauthorized + 404: not found, No resources exist + 500: internet server error, Code error + 502: bad gateway,fastcgi What's coming back web server Don't understand + 503: service unavailable, Service not available + 504: gateway timeout,fastcgi Response timeout

### HTTP Header Fields

Common general head

+ Cache-Control: – no-cache: Do not cache expired caches – no-store: Don't cache + Pragma: no-cache, Do not use cache ,http1.1 Previous history field + Connection: – The control is no longer forwarded to the agent header field – Keep-Alive/Close: Persistent connection + Date: establish http Date of message

Common request headers

+ Accept: Media types and priorities that can be handled + Host: Target host domain name + Referer: Where did the request originate from the original resource URI + User-Agent: The name of the user agent that created the request + Cookie: cookie Information

Common response headers

+ Location: Redirect address + Server: Requested service web server Information about + Set-Cookie: To set up cookie Information – NAME: Key value pairs to set – expires: cookie Expiration time – path: Specify send cookie The catalog of – domain: Specify send cookie Domain name of – Secure: Only https Send next cookie – HostOnly: After designation javascript Can't read cookie + Keep-Alive:

HTTP At the beginning of the agreement, it will be disconnected after each connection TCP Connect , after HEADER Of connection Field definition Keep-Alive（HTTP 1.1 Default 　 Persistent connection ）, Representatives will not disconnect if neither party actively disconnects TCP Connect , It reduces every time you create HTTP When connecting TCP Connection consumption .

## Cookie/Session

+ Cookie: The working mechanism is user identification and state management , In order to manage the user's status, the server will pass through the client , Write some temporary data into the device Set-Cookie, When users access services , The service can retrieve the previously stored cookie. + Session:　 because http It's stateless , Context cannot be maintained between requests , So there it is session As session control , The server stores the user's session information .

## HTTPs

Concept : stay http The agreement adds ssl(secure socket layer) layer .

“` SSL layer | application layer | Transport layer | The network layer | The link layer | Physical layer “`

HTTPS The certification process “`

Initiate request —————————>　　server Issue a certificate <————————— server Certificate digital signature ( Encrypt with certificate authority public key ) —————————>　　 Certification body Certificate digital signature verification passed client( Built in certificate authority certificate ) <————————— Certification body Public key encryption random cipher string ( The shared secret key of the future ) —————————>　　server Private key decryption ( Asymmetric encryption ) SSL End of agreement 　HTTP Agreement start <————————— server( Symmetric encryption ) Shared secret key encryption HTTP —————————>　　server( Symmetric encryption ) “`

+ Check the certificate certificate ： The public secret key of the certificate authority verifies the digital signature of the certificate + Public key encryption establishes a connection ： Asymmetric encryption + Shared key encryption

## Websocket

+ be based on http The protocol establishes the connection ,header Of upgrade The field conversion protocol is websocket + Full duplex communication , The client establishes a connection

## HTTP2

+ Multiplexing ： Multiple requests share one tcp Connect + Full duplex communication + must https:// + The head of compression + Binary transmission

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